<?php

final class DemoFile
{
    public function run(array $params)
    {
        $result = [];
        foreach ($params as $key => $value) {
            if (preg_match('/reg/', $key) > 0) {
                $result[$key] = $value;
            }
        }

        return $result;
    }
}

<?php

final class DemoFile
{
    public function run(array $params)
    {
        return array_filter($params, fn($key) => preg_match('/reg/', $key) > 0, ARRAY_FILTER_USE_KEY);
    }
}